This invention relates to dispersant viscosity index improver concentrates for lubricating oil compositions and to lubricating oil compositions containing the same and to a method of making same. More particularly this invention relates to lubricating oil compositions containing nitrogen modified star polymers of hydrogenated conjugated dienes and to concentrates containing the same and to a method for preparing such modified star polymer concentrates.
U.S. Pat. No. 4,358,565 and EP 029,622 describe lubricating oil compositions containing a grafted star polymer. The star polymers are grafted with a nitrogen-containing polymerizable polar organic compound to improve dispersancy. The preferred nitrogen-containing compounds are 2-vinylpyridine and 4-vinylpyridine. Many other nitrogen-containing compounds are listed in the specification, including N-vinylimidazole and N-vinylpyrrolidone. The specification does not limit the nitrogen content of the compositions.
U.S. Pat. No. 4,820,776 describes lubricating oil compositions containing a grafted diene polymer. The diene polymers are grafted with both a nitrogen-containing polymerizable polar organic compound and a second component. The preferred nitrogen-containing compound is N-vinylpyrrolidone which was used in many of the examples. The specification mentions that 1-vinylimidazole or 4-vinylpyridines can be grafted although the products are not described.
U.S. Pat. No. 4,222,882 describes lubricating oil compositions containing a grafted star polymer. The star polymers are grafted with N-vinylpyrrolidone to improve dispersancy.
U.S. Pat. No. 4,229,308 describes lubricating oil compositions containing a grafted star polymer. The star polymers are grafted with a compound containing two C-N=C segments.
U.S. Pat. Nos. 4,693,838 and 4,780,228 and EP 171,167 describe lubricating oil compositions containing a grafted diene polymer. The diene polymers are grafted with nitrogen containing compounds having at least six carbon atoms such as N-vinylpyrrolidone.
U.S. Pat. No. 4,427,834 describes the polymerization of a nitrogen containing arm to a star polymer. The nitrogen containing arm is polymerized from cyclic momomers such as N-vinylimidazole and N-vinylpyrrolidone.
U.S. Pat. No. 4,699,723 and GB 1601079 describe the grafting of nitrogen containing compounds to olefin copolymers and terpolymers to improve dispersancy in oil compositions.
While it is generally known to prepare viscosity index improvers containing nitrogen, no effort has been made to carefully control the amount of nitrogen contained in the polymer or to obtain the advantages associated therewith. Moreover, no processes have been proposed for such careful control. The need, then, for a viscosity index improver concentrate containing a carefully controlled amount of nitrogen and for lubricating oils containing such a viscosity index improver concentrate and for a method of preparing the same is, then, believed to be readily apparent.